WPLANG_ADMIN and WPLANG_USER

Whenever I download an MO file, it also changes the admin interface, which is not what I want. I want the default English labels and messages in the admin interface, and Swedish (or whatever) labels and messages in the user interface.

I think WP should split the WPLANG variable in two: one for the inside and one for the outside, so we could write something like this in wp-config.php:

define (‘WPLANG_ADMIN’, ‘en_US’);
define (‘WPLANG_USER’, ‘sv_SE’);